Polyphenols are a class of phytochemicals or plant-based chemicals. They are nonessential nutrients for humans but many studies have shown that they may protect against a variety of human diseases. Since they are widespread in fruits and vegetables, it is easy to reap the health benefits of these compounds by increasing consumption of fresh produce. Polyphenols can be further classified as flavonoids and non-flavonoids, according to their chemical composition.
Flavonoids
The flavonoid type polyphenols include anthocyanins, catechins, flavanones, flavones, flavonols and isoflavones. Anthocyanins are found in berries, red and purple grapes and red wine. Catechins are abundant in green and white tea, chocolate, grapes, berries and apples. Some common dietary flavanones are the compounds hesperetin, naringenin, eriodictyol. These are particularly high in citrus fruits such as oranges, grapefruits and lemons. Flavones can be obtained from parsley, thyme, celery and hot peppers. Flavonols are a large group of flavonoid-type polyphenols and are found in many different plant sources. Quercetin is the most widely known flavonol and has been the best-studied. Black and oolong teas and good sources of flavonols as are green vegetables, apples, berries and onions. The isoflavones include daidzein, genistein and glycitein and are high in soybeans and other legumes.
Non-flavonoids
Ellagic acid is a polyphenol found in strawberries, blueberries, raspberries, cranberries, walnuts and pecans. Some studies have demonstrated anti-cancer functions of ellagic acid, but the American Cancer Society cautions that further research is needed to determine the effectiveness in humans. Coumarin is a non-flavonoid polyphenol that is a precursor molecule in anticoagulant medications. It is found in tonka beans, lavender, licorice, strawberries, apricots, cherries, cinnamon, and sweet clover.
Health Benefits
More studies are needed to provide conclusive evidence of polyphenol effectiveness in humans. However, a number of early studies have identified possible health benefits. Polyphenols appear to act as antioxidants, removing harmful free radicals from the body. They may boost the immune system, alter hormone metabolism and aid in the metabolism of vitamin A. The relationship of polyphenols to cancer is an area of active study. Polyphenols may help protect the body from carcinogens and may aid in the repair of mutagenic DNA damage.
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